1. Field of the Invention
The present invention relates to a pneumatic tire with a wide central groove, more particularly to a tread pattern having a specific land ratio arrangement being capable of improving wet performance and steering stability.
2. Description of the Related Art
In the laid-open Japanese patent application Nos. JP-A-6-143932, JP-A-6-143937 and JP-A-6-191227, pneumatic tires with a wide central groove are disclosed, wherein the wide central groove has a width in the range of from 35 to 45 mm and extends on the tire equator continuously in the tire circumferential direction.
In such a tire, when additional grooves are provided, the steering stability is liable to deteriorate because the tread rigidity is already decreased by the wide central groove considerably. From this point of view, it is preferable to decrease the additional grooves. However, if such grooves are decreased, wet performance, especially antiaquaplaning performance greatly decreases.
Therefore, the present inventors studied tread pattern to obtain maximum effect from minimum additional grooves, and found that the steering stability and wet performance become compatible with each other by specifically limiting the distribution of land ratio.
It is therefore, an object of the present invention to provide a pneumatic tire with a wide central groove, in which both the steering stability and wet performance are improved.
According to the present invention, a pneumatic tire comprises
a circumferentially continuously extending wide groove having a width of from 35 to 45 mm disposed in a tread center,
a tread part on each side of the wide groove, which is defined as extending at least 10 mm axially outwards from the groove edge, being formed as a substantially continuous rib part,
a tread part between the rib part and a tread edge, being provided with circumferentially discontinuous grooves so that: an axially inner part has a land ratio La of not less than 90%; a middle part has a land ratio Lb in a range of from 80 to 90%; and an axially outer part has a land ratio Lc in a range of from 85 to 95%, wherein the axially inner part, middle part and axially outer part are three equiwidth parts between the wide groove and the tread edge.
An embodiment of the present invention will now be described in detail in conjunction with the accompanying drawings.
FIG. 1 is a cross sectional view of a pneumatic tire according to the present invention.
FIG. 2 is a developed plan view thereof showing an example of the tread pattern.
FIG. 3 is a foot print thereof.
FIG. 4 is a diagram for explaining the oblique groove.